Specifically, we will study Native American children, and their mothers, so as: 1) to determine the distribution of etiologies of CH in the Native American population using Iodide radionuclide imaging, uptake, and perchlorate discharge testing as indicated. 2) to determine the level of antithyroid antibodies in the mother and baseline thyroid function in both mother and child. 2a) to develop family medical histories addressing autoimmunity and perform a thorough physical exam of each patient with congenital hypothyroidism.